Data burst transmission methods in WLAN devices and systems

ABSTRACT

A wireless local area network (WLAN) device transmits a header over an air interface, at a first modulation rate. The header may include an indication of a second modulation rate that will be used to transmit a consolidated payload. In one embodiment, the header includes information that enables a receiver to determine when an end of each of the multiple data units will occur. The device farther transmits the consolidated payload at the second modulation rate. The consolidated payload includes multiple data units. In one embodiment, the consolidated payload includes information that enables the receiver to determine when an end of each of the multiple data units will occur.

TECHNICAL FIELD

The inventive subject matter pertains to wireless local area networks(WLANs) and, more particularly, to transmission of data packets betweena transmitter and a receiver in a WLAN.

BACKGROUND

Any Wireless Local Area Network (WLAN) device that supports an Instituteof Electrical and Electronics Engineers (IEEE) 802.11 Standard (e.g.,IEEE Std 802.11-1997, 802.11a, 802.11e, etc.) includes two mainparts: 1) a physical (PHY) layer signaling control device; and 2) amedium access control (MAC) device. The function of the PHY device is totransfer data packets over the air interface. Among other things, thefunction of the MAC device is to fairly control access to the shared airinterface.

The minimal MAC protocol consists of two frames: 1) a frame sent from atransmitter to a receiver; and 2) an acknowledgment (ACK) from thereceiver that the frame was received correctly. If a transmitter hasmultiple packets to send to the receiver, some versions of the 802.11Standard require the transmitter to wait for an ACK after transmissionof each packet. In addition, the transmitter must wait for a particulartime interval, referred to as the Interframe Space (IFS), afterreceiving the ACK and before transmitting the next packet.

Other versions of the 802.11 Standard (e.g., IEEE Std 802.11e) supporttransmission of packets with selective acknowledgement. This feature isreferred to as “Block ACK.” The Block ACK feature enables thetransmitter to send the next packet to the same receiver withoutnecessarily waiting for an ACK. Instead, after negotiating for access tothe air interface, the transmitter sends the first packet, waits an IFSafter the end of the first packet, and sends the next packet. After thetransmitter has sent all of its packets to the receiver, the transmitterasks the receiver for a response, which indicates an ACK for all of thepreviously transmitted packets.

Although the Block ACK feature has provided some throughputimprovements, developers continue to strive for ways of furtherincreasing throughput. Accordingly, what are needed are methods andapparatus for further improving throughput using burst-modetransmissions.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims point out different embodiments of the inventivesubject matter with particularity. However, the detailed descriptionpresents a more complete understanding of the inventive subject matterwhen considered in connection with the figures, wherein like-referencenumbers refer to similar items throughout the figures and:

FIG. 1 is a simplified diagram of example WLANs, in accordance with anembodiment of the inventive subject matter;

FIG. 2 is a simplified block diagram of a WLAN station, in accordancewith an embodiment of the inventive subject matter;

FIG. 3 illustrates an example of a timing diagram for transmittingmultiple PHY protocol data unit (PPDU) frames, each with a singleservice data unit (SDU);

FIG. 4 illustrates an example of a timing diagram for transmitting aPPDU that may contain multiple SDUs and delimiters, in accordance withan embodiment of the inventive subject matter;

FIG. 5 is a flowchart of a procedure for a transmitter to assemble andtransmit a PPDU, such as that illustrated in FIG. 4, in accordance withan embodiment of the inventive subject matter;

FIG. 6 is a flowchart of a procedure for a receiver to receive anddivide a PPDU, such as that illustrated in FIG. 4, in accordance with anembodiment of the inventive subject matter;

FIG. 7 illustrates an example of a timing diagram for transmitting aPPDU with multiple SDUs without intervening data in accordance with anembodiment of the inventive subject matter;

FIG. 8 is a flowchart of a procedure for a transmitter to assemble andtransmit a PPDU, such as that illustrated in FIG. 7, in accordance withan embodiment of the inventive subject matter;

FIG. 9 is a flowchart of a procedure for a receiver to receive anddivide a PPDU, such as that illustrated in FIG. 7, in accordance with anembodiment of the inventive subject matter;

FIG. 10 illustrates an example of a timing diagram for transmitting aburst of multiple PPDUs in accordance with an embodiment of theinventive subject matter;

FIG. 11 is a flowchart of a procedure for a transmitter to transmit aburst of multiple PPDUs, such as those illustrated in FIG. 10, inaccordance with an embodiment of the inventive subject matter;

FIG. 12 is a flowchart of a procedure for a receiver to receive a burstof multiple PPDUs, such as those illustrated in FIG. 10, in accordancewith an embodiment of the inventive subject matter;

FIG. 13 illustrates an example of a timing diagram for transmitting aburst of multiple PPDUs with shortened intervening preambles inaccordance with an embodiment of the inventive subject matter;

FIG. 14 is a flowchart of a procedure for a transmitter to transmit aburst of multiple PPDUs, such as those illustrated in FIG. 13, inaccordance with an embodiment of the inventive subject matter;

FIG. 15 is a flowchart of a procedure for a receiver to receive a burstof multiple PPDUs, such as those illustrated in FIG. 13, in accordancewith an embodiment of the inventive subject matter;

FIG. 16 illustrates an example of a timing diagram for transmitting aburst of multiple PPDUs without intervening preambles, in accordancewith an embodiment of the inventive subject matter;

FIG. 17 is a flowchart of a procedure for a transmitter to transmit aburst of multiple PPDUs, such as those illustrated in FIG. 16, inaccordance with an embodiment of the inventive subject matter; and

FIG. 18 is a flowchart of a procedure for a receiver to receive a burstof multiple PPDUs, such as those illustrated in FIG. 16, in accordancewith an embodiment of the inventive subject matter.

DETAILED DESCRIPTION

In the following description of various embodiments, reference is madeto the accompanying drawings, which form a part hereof and show, by wayof illustration, specific embodiments in which the inventive subjectmatter may be practiced. Various embodiments are described in sufficientdetail to enable those skilled in the art to practice the inventivesubject matter, and it is to be understood that other embodiments may beutilized, and that process or mechanical changes may be made, withoutdeparting from the scope of the inventive subject matter. Suchembodiments of the inventive subject matter may be referred to,individually and/or collectively, herein by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any single invention or inventive concept if morethan one is in fact disclosed. It will be recognized that the methods ofvarious embodiments can be combined in practice, either concurrently orin succession. Various permutations and combinations will be readilyapparent to those skilled in the art.

Embodiments of the inventive subject matter include ways of transmittingmultiple packets in a burst mode (i.e., in succession). Variousembodiments will be described in detail below, after a description of awireless local area network (WLAN) system and a WLAN device, inconjunction with FIGS. 1 and 2. Various embodiments can be implementedin systems and devices such as the system and device described inconjunction with FIGS. 1 and 2. Various embodiments also can beimplemented in other systems and devices, which have differentconfigurations.

FIG. 1 is a simplified diagram of example WLANs in accordance with anembodiment of the inventive subject matter. A WLAN may include multiplenetwork stations 102 and zero or more access points (APs) 104.

In a WLAN, network stations 102 communicate over the medium of freespace, commonly referred to as the “air interface.” Generally, a station102 may be referred to as a network adapter or network interface card(NIC). A station 102 may be mobile, portable or stationary. For example,a station 102 may be a laptop computer, a handheld radio, a desktopcomputer, or virtually any other one-way or two-way device with thecapability of communicating with other devices 102 or APs 104 over awireless medium.

A set of stations 102 may communicate directly with each other, as isthe case in a Basic Service Set (BSS). An Independent BSS (IBSS) 110 isa BSS in which there is no connection to a wired network.

An infrastructure BSS 112 is a BSS in which a BSS includes an AP 104. Inan infrastructure BSS, all stations 102 communicate with an AP 104. TheAP 104 provides the connection to the wired LAN, if any, and the localrelay function for the BSS. Accordingly, if a first station 102 wants tocommunicate with a second station 102, the first station 102 sends thecommunication to the AP 104, and the AP 104 relays the communication tothe second station 102.

An Extended Service Set (ESS) 114 is a set of infrastructure BSSs 112,where the APs 104 communicate among themselves to forward traffic fromone BSS 112 to another, and to facilitate the movement of stations 102from one BSS to another. The Distribution System (DS) is a mechanism bywhich one AP 104 communicates with another to exchange frames fromstations 102 in their BSSs 112, forward frames to follow mobile stations102 from one BSS 112 to another, and exchange frames with wirednetworks, if any.

Embodiments of the invention will now be described in more detail.Although various embodiments are described in detail, below, using termsthat are similar to terms used in the context of an IEEE 802.11 Standard(e.g., IEEE Std 802.11-1997, 802.11a, 802.11e, etc.), the invention isnot meant to be limited to use within a system that uses an IEEE 802.11Standard. Instead, embodiments of the invention could be used inconjunction with other WLAN standards, as well.

FIG. 2 is a simplified block diagram of a WLAN station 200 (e.g.,stations 102, 104, FIG. 1) in accordance with an embodiment of theinventive subject matter. Any WLAN station 200 that supports an IEEE802.11 Standard includes a physical (PHY) layer signaling control device202 (PHY device), a medium access control (MAC) device 204, and a MACclient 206. WLAN station 200 supports station services, which areprovided by PHY device 202 and MAC device 204, and used by MAC client206. These services may include authentication, deauthentication,privacy, and delivery of data.

The MAC client 206 creates and processes data, among other things. Thepurpose of the PHY and MAC devices 202, 204 is to ensure that twonetwork stations are communicating with the correct frame format andprotocol. An IEEE Std 802.11 defines the communication protocol betweenthe PHY and MAC devices 202, 204.

The function of the PHY device 202 is threefold: 1) to provide a frameexchange between the MAC 204 and PHY 202 under the control of a physicallayer convergence procedure (PLCP) sublayer; 2) to transmit data framesover the air interface under the control of the physical mediumdependent (PMD) sublayer; and 3) to provide a carrier sense indicationback to the MAC 204 so the MAC 204 is able to verify activity on the airinterface.

The PHY device 202 implements one of several physical layerspecifications, such as infrared (IR) baseband, frequency hopping spreadspectrum (FHSS), direct sequence spread spectrum (DSSS), or orthogonalfrequency domain multiplexing (OFDM). Other specifications can beimplemented in other embodiments.

In general, the PHY device 202 includes PLCP apparatus 210, and transmitand receive PMD apparatuses 212, 214. Each of these may or may not usesome or all of the same physical circuitry (e.g., processors, busses,clocks, storage, etc.). In addition, one or more antennae 216 may beinterconnected with PMD apparatus 212, 214. When an IR basebandspecification is implemented, a light-emitting diode (LED) (not shown)or other optical transmission device may be used instead of the antennae216.

As mentioned above, a function of PLCP apparatus 210 is to control theframe exchange between the MAC device 204 and the PHY device 202. Thefunction of PMD apparatuses 212, 214 is to control signal carrier andspread spectrum modulation and demodulation for transmitting andreceiving data frames over the air interface.

The structures of PMD apparatuses 212, 214 depend on the particularphysical layer specification (e.g., the modulation type) implemented inthe station. For example, if DSSS is used, the transmit PMD apparatus212 may include a scrambler, an adder, a mask filter, and a DBPSK DQPSKmodulator, and the receive PMD apparatus 214 may include a de-spreadcorrelator, a DBPSK DQPSK de-modulator, a de-scrambler, and a timingclock recovery device. If FHSS is used, the transmit PMD apparatus 212may include a data whitener, a symbol mapper, a Gaussian shaping filter,and a modulator, and the receive PMD apparatus 214 may include ade-modulator, a data de-whitener, and a hop timing recovery device. IfIR is used, the transmit PMD apparatus 212 may include a symbol mapper,a modulator, and an LED driver, and the receive PMD apparatus 214 mayinclude a diode detector, a de-modulator, and a symbol mapper. If OFDMis used, the transmit PMD apparatus 212 may include a convolutionalencoder, a bit interleaving and mapping device, an inverse fast Fouriertransform (FFT), a symbol shaper, and a quadrature amplitude modulation(QAM) modulator, and the receive PMD apparatus 214 may include a PSK QAMde-modulator, an FFT, a bit de-interleaving and de-mapping device, aconvolutional decoder, and a clock recovery device.

Among other things, the function of the MAC device 204 is to controlaccess to the shared air interface. The MAC device 204 provides aninterface between the MAC client 206 and the PHY device 202. Inaddition, the MAC device 204 may or may not perform encryption anddecryption. In on embodiment, the MAC device supports the MAC sublayeraccording to an IEEE Std 802.11. In other embodiments, the MAC devicesupports the MAC sublayer according to another standard.

Because the air interface is often very noisy and unreliable, an IEEEStd 802.11 MAC device 204 implements a frame exchange protocol to allowthe source of a data frame to determine whether the frame has beensuccessfully received at the destination. The minimal MAC protocolconsists of two frames: 1) a sent frame that includes a frame sent fromthe transmitter to the receiver; and 2) a response frame that includesan acknowledgment (ACK) from the receiver that the sent frame wasreceived correctly. In addition, a sent frame might be one of thefollowing: an acknowledgement (ACK), a request to send (RTS), a clear tosend (CTS), or a PS-Poll. The corresponding response frames would be,respectively: a fragment; a CTS; a data frame; and an ACK.

FIG. 3 illustrates an example of a timing diagram for transmittingmultiple PHY protocol data unit (PPDU) frames, each carrying a singleservice data unit (SDU). The PPDU frames 300, 310 represent the formatof a frame as it is transmitted over the air interface. A PPDU frameincludes a preamble 302, a PHY header 304, and a SDU 306, in anembodiment.

The preamble 302, the PHY header 304, and the SDU 306 each aretransmitted at the beginning of a symbol boundary, as indicated by thetic marks on the time axis 320 of FIG. 3. Each symbol may have apre-determined duration, or a duration that changes within differentparts of the packet. For example, a symbol duration may be 4microseconds, although it can be longer or shorter, as well.

The preamble 302 includes a pattern of bits, which the receiver uses tosynchronize itself. Specifically, the receiver may use the preamble 302to perform the following tasks: 1) packet start acquisition; 2) channelestimation; 3) antenna diversity and training; 4) receiver automaticgain control (AGC); 5) carrier offset; and 6) symbol timing.

Within the PHY header 304 are a rate field and a length/size field, inone embodiment. The rate field indicates which type of modulation mustbe used to receive the incoming SDU 306. In an alternate embodiment, therate of the incoming SDU 306 is determined in advance between atransmitting and receiving station, and thus the rate information maynot be included in the PHY header 304.

The length/size field indicates the length of the SDU 306. In variousembodiments, the length/size field can include a number of microsecondsnecessary to transmit the SDU 306, a number of bytes in the SDU 306, orsome other value indicating the length of the SDU 306. The PHY header304 may also include a checksum or other field, which enables itscontents to be validated. The PHY header 304 could have a fixed orvariable length.

The SDU 306 is a series of fields that is assembled by the MAC 204 (FIG.2) and passed to the PHY 202 via PLCP 210. As far as the PHY 202 isconcerned, the SDU 306 includes “opaque data,” meaning that the PHY 202does not know or care what data is included in the SDU 306.

The SDU 306 can be of a variable length. An SDU frame may be used by theMAC device 204 to transport its MAC protocol data unit (MPDU), which mayinclude an MPDU header, a frame body field, and a frame check sequence(FCS) field. The frame body field is of a variable length, and itscontents may or may not be encrypted. This field may contain all or partof a MAC service data unit (MSDU) or protocol service data unit (PSDU)from higher layer protocols.

Different modulation rates may be used to transmit the preamble 302, PHYheader 304, and SDU 306. The preamble 302 and PHY header 304 aretransmitted at a first rate, referred to herein as a “robust modulationrate.” The robust modulation rate may be in a range of approximately 6megabits per second (Mbps) to 12 Mbps, in an embodiment, although rateshigher or lower can be used in other embodiments. The robust modulationrate does not change, in an embodiment. When the robust modulation ratedoes not change, a receiver knows to look for a preamble 302 and PHYheader 304 at the known robust modulation rate. In another embodiment,the robust modulation rate may change. In still another embodiment, thepreamble 302 and the PHY header 304 are transmitted at differentmodulation rates.

In contrast, the SDU 306 may be transmitted at a second rate, referredto herein as a “data modulation rate.” For illustration purposes, theSDU 306 is cross-hatched, indicating that it is transmitted at the datamodulation rate, as opposed to the robust modulation rate.

The data modulation rate can vary from frame to frame. In an embodiment,the rate varies in a range of between approximately 6 to 240 Mbps. Inone embodiment, a receiver determines the data modulation rate for aparticular SDU by evaluating the rate field of the PHY header 304, asdescribed above.

The lower modulation rates may be more robust, meaning that the data cantolerate worse channel conditions. The preamble 302 and PHY header 304are sent at the lower modulation rate, so that the data within the PHYheader 304 is less likely to be corrupted, even though corruption ispossible given enough interference signal power. If the data within therate field of the PHY header 304 were corrupted, for example, thereceiver would be unable to demodulate the SDU 306. If the data withinthe size field of the PHY header 304 were corrupted, the receiver wouldeither truncate the SDU 306 or would extend the SDU 306, causing thereceiver to demodulate invalid data after the end of the SDU 306.

The data modulation rate for the SDU 306 can be chosen based on anestimate of channel conditions. If the channel is excellent, then a highrate (e.g., approaching 240 Mbps) may be selected, thus increasing thethroughput of the system. If the channel is very noisy, then arelatively low rate (e.g., approaching 6 Mbps) may be selected, so thatthe data integrity can be maintained as best possible.

In various embodiments, each packet is fully or partially“self-describing,” meaning that the receiver does not need a prioriinformation about the structure (i.e., the data rate and/or size) of theupcoming packet. In one embodiment, each packet is fullyself-describing, meaning that each packet includes both the datamodulation rate, in the PHY header 304, and also the length/sizeinformation. The length/size information is included in the PHY header304, in one embodiment, and in the SDU itself, in another embodiment.

In another embodiment, each packet is partially self-describing, meaningthat each packet includes the length/size information, but the datamodulation rate may be defined between the transmitting and receivingstation in a prior training exchange. Accordingly, the data modulationrate is not necessarily included in the PHY header 304.

This “self-describing” feature differentiates embodiments of theinvention from other protocols, such as the Hiperlan 2 protocol, forexample. Using the Hiperlan 2 protocol, the transmitter emits a knownblock of data every 2 milliseconds. That block of data includes acomplete map of everything that the transmitter will transmit for theremainder of the upcoming 2 millisecond time period. This means that allreceivers have a priori information about the modulation rates andlengths of the packets that the transmitter will send. The modulationand length information is not included in each packet, using Hiperlan 2,and thus the packets are not “self-describing.”

As discussed previously, prior art systems support “burst-mode”transmission of PPDU frames with selective acknowledgement using the“Block ACK” feature. The Block ACK feature enables the transmitter tosend the next PPDU frame to the same receiver without necessarilywaiting for an ACK. Instead, after negotiating for access to the airinterface, the transmitter sends the first PPDU frame, waits anInterframe Space (IFS) after the end of the first packet, and sends thenext PPDU frame.

The term “IFS,” as used herein, is meant to include various related timeperiods, including but not limited to the IFS, a Short IFS (SIFS), aPriority IFS (PIFS), a Distributed IFS (DIFS), and an Extended IFS(EIFS), as defined in an IEEE 802.11 Standard, although the term IFS isnot meant to be limited to time periods defined only in such a standard.The IFS may consume multiple symbol boundaries. FIG. 3 illustrates asecond PPDU 310 being transmitted after a symbol gap 312 of four or moresymbols, which can represent an IFS. An IFS can be an integer ornon-integer number of symbol widths. In addition, the duration of theIFS can be longer or shorter than four symbols.

Using the Block ACK feature, after the transmitter has sent all of itsPPDU frames to the receiver, the transmitter asks the receiver for aresponse, which indicates an ACK for all of the previously transmittedframes. Using prior art methods, each PPDU frame includes a single SDU,and each PPDU frame is formatted essentially as described in conjunctionwith FIG. 3.

In accordance with various embodiments of the inventive subject matter,a single PPDU frame includes one or more opaque, concatenated SDUs,where the one or more SDUs are referred to herein as the “payload.” Inan embodiment, each SDU includes a “delimiter,” which indicates the sizeof the SDU, and the PHY header may include a length field that includesthe entire length of the concatenated SDUs. In another embodiment, thePHY header contains length information for each SDU, enabling thereceiver to assemble and re-divide the payload into the distinct SDUs.

In still another embodiment, each PPDU frame includes a single SDU.However, during burst mode, multiple PPDU frames are concatenatedtogether, rather than waiting the IFS between each frame. In stillanother embodiment, multiple PPDU frames are concatenated together, buta shortened preamble is included with each PPDU frame after the firstframe. In still another embodiment, multiple PPDU frames areconcatenated together, but the preamble is eliminated for each PPDUframe after the first frame. Various embodiments will now be describedin conjunction with FIGS. 4-18.

FIG. 4 illustrates an example of a timing diagram for transmitting aPPDU that may contain multiple SDUs and delimiters, in accordance withan embodiment of the inventive subject matter. The PPDU 400 includes apreamble 402, PHY header 404, and a consolidated payload 406 with atleast one SDU 420, 422, 424. In the illustrated example, theconsolidated payload 406 includes three SDUs. More or fewer SDUs can beincluded in a single payload.

The preamble 402 includes a pattern of bits, which the receiver uses tosynchronize itself, as described above. The PHY header 404 includes arate field, in one embodiment, which indicates which data modulationrate is used for the consolidated payload 406. In an embodiment, the PHYheader 404 also includes a length/size field, which defines the totallength of the consolidated payload 406. In various embodiments, thelength/size field can include a number of microseconds necessary totransmit the consolidated payload 406, a number of bytes in theconsolidated payload 406, or some other value indicating the length ofthe consolidated payload 406. In another embodiment, the PHY header 404does not include the total length information. The PHY header 404 couldhave a fixed or variable length.

Each SDU 420, 422, 424 must be separated and delivered intact by the PHYin the receiver. To facilitate decomposition of the consolidated payload406 into individual SDUs, the consolidated payload also includesinformation indicating the lengths of each of the multiple SDUs. In anembodiment, the information includes multiple “delimiters” 408, 410,412, where each SDU is preceded by a delimiter, in an embodiment.

Each delimiter includes a length field, which indicates the variablelength 430, 432, 434 of the SDU 420, 422, 424, respectively, thatfollows. If the following SDU is not the last SDU in the consolidatedpayload 406, the delimiter information also enables a receiver todetermine where the next SDU's delimiter should be located.

In an embodiment, each delimiter 408, 410, 412 also includes a lengthvalidation field, which enables a receiver to determine whether or notthe length field has been corrupted, as described in more detail later.In an embodiment, the length validation field includes a checksum orCRC, although other validation information can be used in otherembodiments. The length validation field enables robust error detection,as will be described in detail in conjunction with FIGS. 5 and 6.

In addition, in an embodiment, each delimiter 408, 410, 412 may alsoinclude a sequence field, which indicates that the SDU 420, 422, 424,respectively, that follows is either the last SDU or is not the lastSDU. In other embodiments, the delimiter may not include either or boththe length validation field or the sequence field.

In an embodiment described above, a one-to-one correlation existsbetween delimiters and SDUs. In another embodiment, a one-to-onecorrelation may not exist between delimiters and SDUs. Instead, a fewernumber of delimiters than the number of SDUs can be transmitted. Forexample, a single delimiter can be transmitted, which indicates thelengths of all of the SDUs.

FIG. 5 is a flowchart of a procedure for a transmitter to assemble andtransmit a PPDU, such as that illustrated in FIG. 4, in accordance withan embodiment of the inventive subject matter. The method begins, inblock 502 when the PHY device obtains at least one SDU. In oneembodiment, the SDUs are intermediately or finally destined for the samereceiver, although it is possible for the SDUs to have differentdestinations.

In block 504, the lengths of each SDU and length validation data aredetermined. For example, in an embodiment, the SDU length is representedby two bytes, and the length validation field includes a checksum or CRCfor the two-byte length field. Accordingly, the length validation fieldalso can be two bytes. In other embodiments the length and/or lengthvalidation fields can be larger or smaller.

The delimiters for each SDU are assembled, in an embodiment, in block506. Each delimiter includes the length field, the length validationfield, and a sequence field, which indicates whether or not the SDU isthe last. In other embodiments, either or both the length validationfield or the sequence field can be excluded from the delimiter.

In an embodiment, the total length of the consolidated payload isdetermined, in block 508, for inclusion in the PHY header. The totallength includes the lengths of each of the delimiters, plus the lengthsof each of the SDUs. The total length enables the receiver to determinewhen the end of the consolidated payload should occur. In anotherembodiment, the total length is not included in the PHY header. Forexample, in another embodiment, the receiver can rely instead on thesequence field of the delimiter to predict the end of the consolidatedpayload. As will be explained in more detail later, if a delimiter iscorrupted, the receiver may measure the symbol energy to determinewhether the end of the consolidated payload has been reached.

After negotiating access to the air interface, the transmitter transmitsthe preamble and the PHY header over the air at the robust modulationrate, in block 510. In an embodiment, the transmitter beginstransmitting each of the preamble and the PHY header at the beginning ofa symbol boundary. In an embodiment, the preamble is transmitted for twosymbols, and the PHY header is transmitted for one symbol. In otherembodiments, either the preamble or the PHY header can be transmittedfor longer or shorter time durations.

When transmission of the PHY header is complete, the transmitterswitches to the data modulation rate, in block 512, which will be usedto transmit the consolidated payload. The transmitter beginstransmitting the first delimiter, in block 514. In an embodiment, thetransmitter begins transmitting the first delimiter at the beginning ofthe next symbol boundary after completion of the PHY header.Alternatively, the first delimiter can begin at a time other than asymbol boundary. In other words, transmission can begin before or aftera symbol boundary. In an embodiment, the transmitter begins transmittingthe consolidated payload within one symbol width of the end of the PHYheader. Internal block padding may be included at the end of each SDU.

In an embodiment, the delimiter may take less than one symbol tocomplete, and the transmitter may begin to transmit the SDU within thelatter part of the same symbol as the delimiter. In another embodiment,the transmitter begins transmitting the SDU at the next symbol boundaryafter completion of the delimiter transmission. Internal block paddingmay be included at the end of each SDU.

In block 516, a determination is made whether more delimiters and SDUsremain to be transmitted. In another embodiment, this determination canbe excluded. If more delimiters and SDUs remain to be transmitted, thetransmitter begins transmitting the next delimiter and its associatedSDU, in block 514.

In an embodiment, the transmitter begins transmitting the next delimiterpromptly upon completion of transmitting the previous SDU, whether ornot that time occurs on a symbol boundary. In addition, the transmitterbegins transmitting the associated SDU promptly upon completion oftransmitting the delimiter. Accordingly, in this embodiment, all of thedata within the consolidated payload is efficiently concatenatedtogether. In other embodiments, gaps or filler data can exist betweensubsequent delimiters and/or SDUs. After transmitting the last SDU, themethod ends.

FIG. 6 is a flowchart of a procedure for a receiver to receive anddivide a PPDU, such as that illustrated in FIG. 4, in accordance with anembodiment of the inventive subject matter. The method begins, in block602, when the receiver detects an incoming preamble at the robustmodulation rate. The receiver uses the preamble to become synchronizedwith the incoming PPDU frame, in block 604.

In one embodiment, the receiver determines the modulation rate of thePPDU's consolidated payload from the PHY header, in block 606. In analternate embodiment, the data modulation rate may be determined duringa prior training exchange.

In an embodiment, the receiver also determines the entire length of theconsolidated payload from the PHY header. This enables the receiver toknow how long it should demodulate incoming data at the data modulationrate. In another embodiment, the receiver uses the length and sequencefields in the delimiters to make this determination, and the totallength is not necessarily provided in the PHY header. Once receipt ofthe PHY header has completed, the receiver switches to demodulating atthe data modulation rate, in block 608, in order to receive anddemodulate the consolidated payload.

The first thing that occurs in the consolidated payload is a delimiter,in an embodiment. Therefore, in block 610, the receiver receives andattempts to validate a segment of data having the size of a delimiter.In an embodiment, the delimiter size is the size of the length field(e.g., two bytes), plus the size of the length validation field (e.g.,two bytes), plus the size of the sequence field (e.g., one byte), if itis included. In other embodiments, the absolute or relative sizes of thevarious delimiter fields can be different.

Validation is performed by determining if the length validation fieldcorrelates with the data in the length field. In an embodiment, thelength validation field includes a checksum or CRC, which enables thereceiver to determine whether the length data is corrupted oruncorrupted.

A determination is made, in block 612, whether the delimiter-sized datasegment includes what appears to be a valid delimiter. If so, then inblock 614, the receiver receives and stores an amount of SDU data with alength as indicated in the delimiter's length field, and the methodproceeds to block 622, which will be described later.

If the delimiter-sized segment does not include what appears to be avalid delimiter, then the receiver transitions to a delimiter searchmode, indicated by blocks 616, 618, and 620. In this mode, the receiverdetermines whether the end of the payload may have been reached, inblock 616. In various embodiments, the end of the payload can bedetermined if no delimiter is detected within an amount of time, or if aknown end point has been reached, or if the symbol energy drops below athreshold. If the end of the payload has been reached, the method ends.

If the end of the payload has not been reached, then the receiverreceives and evaluates each subsequent delimiter-sized segment of data,in block 618. Subsequent segments can be overlapping or sequential.

A determination is made, in block 620, whether the next delimiter-sizedsegment of data appears to be a possible delimiter by validating whatcan be the length field with what can be the length validation field. Ifthe delimiter-sized segment of data does not appear to be a possibledelimiter, then the procedure iterates, all the while storing thereceived data as a potential SDU. When a possible delimiter is detected,the receiver discontinues the delimiter search mode.

A determination is made, in block 622, whether the end of theconsolidated payload has been reached. In an embodiment, the receiverknows that it has reached the end of the consolidated payload if it hasreceived an amount of data that corresponds to the total length fieldprovided in the PHY header. In another embodiment, the receiver knowsthat it has reached the end of the consolidated payload if it hasreceived an amount of data indicated in the last delimiter as the lengthof the last SDU. In an embodiment, the receiver knows whether or not anSDU is the last SDU of the consolidated payload by evaluating thesequence field of the last SDU's delimiter. In other embodiments, eitheror both the total length field in the PHY header or the sequence fieldin the delimiter can be excluded, and another way of determining the endof the consolidated payload can be used. For example, the receiver maymeasure the symbol energy to determine whether the end of theconsolidated payload has been reached.

If the end of the consolidated payload has not yet been reached, theprocedure iterates as shown. Specifically, the receiver evaluates thenext delimiter-sized data segment, in block 610, and the procedurerepeats.

If the end of the consolidated payload has been reached, the receiverdelivers the various SDUs that it parsed from the consolidated payload,in block 624, and the method ends. In another embodiment, the receivercan deliver each SDU while the SDU is being received, or in parallelwith receiving other SDUs.

Embodiments described above in conjunction with FIGS. 4-6 provide a highthroughput method of burst-mode transmission with robust error detectionand recovery. Throughput is improved from prior art methods byeliminating the IFS between SDUs, as well as by eliminating interveningpreambles and PHY headers associated with SDUs that occur after thefirst SDU.

The length validation field enables robust error detection and recovery.First, the length validation field enables the receiver to determinewhether the length field is corrupted in the delimiter. If the receiverdetermines that the length field is corrupted, the receiver can look atevery byte that follows, to try to find a segment of data that appearsto be a delimiter. If the receiver finds a segment of data that appearsto be a delimiter, the receiver assumes that the data represents adelimiter, and the receiver re-synchronizes itself for receipt of thenext SDU.

In an embodiment, the chance is very slim of the receiver finding a datasegment that appears to be a delimiter, but is not. In an embodimentthat includes a 2-byte CRC, the chance of incorrectly detecting adelimiter is approximately 1 in 65,000. Even if this occurs, thereceiver will again detect an error when it does not find a validdelimiter at the end of the supposed SDU. And again, the receiver willsearch for a data segment that appears to be a delimiter. Therefore,even if a delimiter is corrupted, and another data segmentcoincidentally looks like a delimiter, the receiver eventually willrecover when it finds a valid delimiter. Accordingly, this embodimentprovides a robust method of error detection and recovery.

In another embodiment, the delimiter includes only a length field, andthe length validation field is excluded. This embodiment works well whenthe channel is robust, and the delimiter's length field is highlyunlikely to be corrupted. If the data in the length field is more likelyto be corrupted, then the lack of a length validation field may make itmore difficult for the receiver to recover from an error in the lengthvalidation field. The receiver may look for a next delimiter based onthe corrupted length, and it would likely find only random data there,which would cause it to be even more difficult for the receiver torecover from the erroneous data.

In an embodiment described in conjunction with FIGS. 6-8, the delimiteris transmitted at the data modulation rate. Although this may increasethe chance that the delimiter's length field might become corrupted, thedelimiter's length validation field enables robust error detection andrecovery.

In another embodiment, described in conjunction with FIGS. 7-9, the PPDUframe may include multiple SDUs, but the length of each SDU is includedin the PHY header, and thus it is transmitted at the robust modulationrate. In this embodiment, the chance that the SDU length fields will becorrupted is less than it would be if the lengths were transmitted atthe data modulation rate.

FIG. 7 illustrates an example of a timing diagram for transmitting aPPDU with multiple SDUs without intervening data in accordance with anembodiment of the inventive subject matter. The PPDU 700 includes apreamble 702, PHY header 704, and a consolidated payload with at leastone SDU 706, 716, 726. In the illustrated example, the consolidatedpayload includes three SDUs. More or fewer SDUs can be included in asingle consolidated payload.

The preamble 702 includes a pattern of bits, which the receiver uses tosynchronize itself, as described above. The PHY header 704 includes arate field, which indicates which data modulation rate is used for theconsolidated payload. The PHY header 704 could have a fixed or variablelength.

Each SDU 706, 716, 726 must be separated and delivered intact by the PHYin the receiver. To facilitate decomposition of the consolidated payloadinto individual SDUs, the PHY header 704 also includes a length/sizefield associated with each SDU 706, 716, 726 included in theconsolidated payload, in an embodiment.

Each length/size field indicates the length of its associated SDU, in anembodiment. In another embodiment, the length/size field defines theaggregate length of the associated SDU and any preceding SDUs within theconsolidated payload. Thus, the length of SDU 706 would be representedas the length 730 of SDU 706. The length of SDU 716 would be representedas the aggregate length 732 of SDU 706 and 716. Finally, the length ofSDU 726 would be represented as the aggregate length 734 of SDUs 706,716, and 726. In various embodiments, the length/size field can includea number of microseconds, a number of bytes, or some other valueindicating length.

The values in the length/size fields enable the receiver to determinewhere one SDU ends, and another begins. Accordingly, in yet anotherembodiment, the length/size field can instead include an “offset” value,which indicates the magnitude of an offset into the consolidated payloadwhere the beginning of the next SDU occurs (or where the end of aprevious SDU occurs).

FIG. 8 is a flowchart of a procedure for a transmitter to assemble andtransmit a PPDU, such as that illustrated in FIG. 7, in accordance withan embodiment of the inventive subject matter. The method begins, inblock 802 when the PHY device obtains at least one SDU. In oneembodiment, the SDUs are intermediately or finally destined for the samereceiver, although it is possible for the SDUs to have differentdestinations.

In block 804, the lengths (or offsets) associated with each SDU aredetermined. The lengths can be the individual length of each SDU, or theaggregate length of each SDU within the consolidated payload. Forexample, in an embodiment, the SDU length is represented by two bytes.In other embodiments the length field can be larger or smaller. In stillother embodiments, an offset value can be used to enable a determinationof the end of one SDU and the beginning of a next SDU, rather than usinga length value.

Each of the lengths or offsets is included in the PHY header.Accordingly, if the consolidated payload includes three SDUs, the PHYheader would include at least three length fields. In one embodiment,the PHY header is fixed in size, which limits the number of SDUs thatthe PHY header may describe. In another embodiment, the PHY header has avariable size. In such an embodiment, the PHY header may includeinformation that enables a determination of how many SDUs the PHY headerdescribes and/or the length of the PHY header.

After negotiating access to the air interface, the transmitter transmitsthe preamble and the PHY header over the air at the robust modulationrate, in block 806. In an embodiment, the transmitter beginstransmitting each of the preamble and the PHY header at the beginning ofa symbol boundary. In an embodiment, the preamble is transmitted for twosymbols, and the PHY header is transmitted for one symbol. In otherembodiments, either the preamble or the PHY header can be transmittedfor longer or shorter time durations.

When transmission of the PHY header is complete, the transmitterswitches to the data modulation rate, in block 808. The transmitterbegins transmitting the first SDU, in block 810. In an embodiment, thetransmitter begins transmitting the first SDU at the beginning of thenext symbol boundary after completion of the PHY header. Alternatively,the first SDU can begin at a time other than a symbol boundary. In otherwords, transmission can begin before or after a symbol boundary. In anembodiment, the transmitter begins transmitting the consolidated payloadwithin one symbol width of the end of the PHY header. Internal blockpadding may be included at the end of each SDU.

In block 812, a determination is made whether more SDUs remain to betransmitted. If more SDUs remain to be transmitted, the transmitterbegins transmitting the next SDU, in block 810. In an embodiment, thetransmitter begins transmitting the next SDU immediately upon completionof transmitting the previous SDU, whether or not that position withinthe payload occurs on a symbol boundary. Accordingly, in thisembodiment, all of the data within the consolidated payload isefficiently concatenated together. In other embodiments, gaps or fillerdata can exist between subsequent SDUs. After transmitting the last SDU,the method ends.

FIG. 9 is a flowchart of a procedure for a receiver to receive anddivide a PPDU, such as that illustrated in FIG. 7, in accordance with anembodiment of the inventive subject matter. The method begins, in block902, when the receiver detects an incoming preamble at the robustmodulation rate. The receiver uses the preamble to become synchronizedwith the incoming PPDU frame, in block 904.

In one embodiment, the receiver determines the modulation rate of thePPDU's consolidated payload from the PHY header, in block 906. In analternate embodiment, the data modulation rate may be determined in aprior training exchange.

In an embodiment, the receiver also determines the lengths or offsetsassociated with each SDU in the consolidated payload from the PHYheader. This enables the receiver to know where the SDU boundariesoccur, and how long it should demodulate incoming data at the datamodulation rate. Once receipt of the PHY header has completed, thereceiver switches to demodulating at the data modulation rate, in block908.

In block 910, the receiver receives and stores an amount of SDU datawith a length as indicated in the associated length field for the SDU inthe PHY header. A determination is made, in block 912, whether the endof the consolidated payload has been reached. In an embodiment, thereceiver knows that it has reached the end of the consolidated payloadif it has received an amount of data that corresponds to the lengthfield for the last SDU provided in the PHY header, whether that lengthfield indicates the length of the last SDU separately, or whether thatlength field indicates the aggregate length. In an alternate embodiment,the receiver may determine that the end of the payload has been reachedusing a measurement of symbol energy.

If the end of the consolidated payload has not yet been reached, theprocedure iterates as shown. Specifically, the receiver receives andstores the next SDU, in block 910, and the procedure repeats.

If the end of the consolidated payload has been reached, in block 914,the receiver delivers the various SDUs that it parsed from theconsolidated payload, and the method ends. In another embodiment, thereceiver can deliver each SDU while the SDU is being received, or inparallel with receiving other SDUs.

In embodiments described in conjunction with FIGS. 7-9, no preambles orPHY headers are transmitted between SDUs. Accordingly, it is notnecessary for the receiver to switch back and forth between the datamodulation rate and the robust modulation rate while the receiver isreceiving the consolidated payload. In another embodiment, illustratedin conjunction with FIGS. 10-12, a preamble and PHY header aretransmitted for each SDU. However, the transmitter does not wait for theIFS before transmitting subsequent PPDU frames that are intermediatelyor finally destined for the same receiver. Instead, the transmitterbegins transmitting the next PPDU frame at the next symbol boundaryafter completion of a previous frame.

FIG. 10 illustrates an example of a timing diagram for transmittingmultiple PPDUs in accordance with an embodiment of the inventive subjectmatter. Each PPDU 1000, 1010, 1020 includes a preamble 1002, 1012, 1022,PHY header 1004, 1014, 1024, and an SDU 1006, 1016, 1026. In theillustrated example, three concatenated PPDUs are shown. More or fewerPPDUs can be sent in accordance with embodiments described inconjunction with FIGS. 10-12.

Each preamble 1002, 1012, 1022 includes a pattern of bits, which thereceiver uses to synchronize itself, as described above. Each PHY header1004, 1014, 1024 includes a rate field, which indicates which datamodulation rate is used for the payload. The data modulation rate may ormay not be the same for each payload. In addition, each PHY header 1004,1014, 1024 includes a length/size field for the SDU 1006, 1016, 1026that follows it. The lengths of the payloads may or may not be the same.Each length/size field indicates the length of its associated SDU, in anembodiment. In various embodiments, the length/size field can include anumber of microseconds, a number of bytes, or some other valueindicating length. The PHY header 1004 could have a fixed or variablelength.

FIG. 11 is a flowchart of a procedure for a transmitter to transmit aburst of multiple PPDUs, such as those illustrated in FIG. 10, inaccordance with an embodiment of the inventive subject matter. Themethod begins, in block 1102 when the PHY device obtains at least oneSDU. In one embodiment, the SDUs are intermediately or finally destinedfor the same receiver, although it is possible for the SDUs to havedifferent destinations.

In block 1104, the length associated with the next SDU to be transmittedis determined. For example, in an embodiment, the SDU length isrepresented by two bytes. In other embodiments the length field can belarger or smaller. The length is included in the PHY header for thatSDU.

After negotiating access to the air interface, the transmitter transmitsthe preamble and the PHY header for the SDU over the air at the robustmodulation rate, in block 1106. In an embodiment, the transmitter beginstransmitting each of the preamble and the PHY header at the beginning ofa symbol boundary. In an embodiment, the preamble is transmitted for twosymbols, and the PHY header is transmitted for one symbol. In otherembodiments, either the preamble or the PHY header can be transmittedfor longer or shorter time durations.

When transmission of the PHY header is complete, the transmitterswitches to the data modulation rate, in block 1108. The transmitterbegins transmitting the first SDU, in block 1110. In an embodiment, thetransmitter begins transmitting the first SDU at the beginning of thenext symbol boundary after completion of the PHY header. Alternatively,the first SDU can begin at a time other than a symbol boundary. In otherwords, transmission can begin before or after a symbol boundary.Although not illustrated in FIG. 11, the last symbol in which an SDU istransmitted can be only partially used. In such a case, a gap may existbetween the end of the SDU and the beginning of the next symbolboundary. In addition, internal block padding may be included at the endof each SDU.

In block 1112, a determination is made whether more SDUs remain to betransmitted. If more SDUs remain to be transmitted, then the procedureiterates as shown. Specifically, the transmitter prepares and transmitsthe next preamble, PHY header, and SDU.

In an embodiment, the transmitter begins transmitting the preamble forthe next PPDU at the beginning of the next symbol boundary aftercompletion of the previous SDU. Alternatively, the next PPDU can beginat a time other than a symbol boundary. In other words, transmission canbegin before or after a symbol boundary. After transmitting the lastSDU, the method ends.

FIG. 12 is a flowchart of a procedure for a receiver to receive a burstof multiple PPDUs, such as those illustrated in FIG. 10, in accordancewith an embodiment of the inventive subject matter. The method begins,in block 1202, when the receiver detects an incoming preamble at therobust modulation rate. The receiver uses the preamble to becomesynchronized with the incoming PPDU frame, in block 1204.

In one embodiment, the receiver determines the modulation rate of thePPDU's payload from the PHY header, in block 1206. In anotherembodiment, the data modulation rate may be determined during a priortraining exchange.

The receiver also determines the length of the associated SDU from thePHY header, in one embodiment. Once receipt of the PHY header hascompleted, the receiver switches to demodulating at the data modulationrate, in block 1208.

In block 1210, the receiver receives and stores an amount of SDU datawith a length as indicated in the associated length field for the SDU inthe PHY header. In an alternate embodiment, the receiver may determinethat the end of the payload has been reached using a measurement ofsymbol energy.

When the end of the SDU has been reached, in block 1212, the receiverdelivers the SDU. In another embodiment, the receiver can begin deliveryof the SDU while the SDU is being received. The procedure then iteratesas shown, by the receiver attempting to detect a preamble at the robustmodulation rate, in block 1202.

In embodiments described in conjunction with FIGS. 10-12, a full-lengthpreamble and PHY header is transmitted between SDUs. In anotherembodiment, illustrated in conjunction with FIGS. 13-15, a full-lengthpreamble is transmitted for the first PPDU frame, and partial preamblesare transmitted for subsequent PPDU frames.

FIG. 13 illustrates an example of a timing diagram for transmitting aburst of multiple PPDUs with shortened intervening preambles inaccordance with an embodiment of the inventive subject matter. The firstPPDU 1300 includes a full-length preamble 1302, and subsequent PPDUs1310, 1320 in the burst include partial preambles 1312, 1322, in anembodiment.

The full-length preamble 1302 includes a pattern of bits, which thereceiver uses to synchronize itself. Specifically, the receiver may usethe preamble 1302 to perform the following tasks: 1) packet startacquisition; 2) channel estimation; 3) antenna diversity and training;4) receiver automatic gain control (AGC); 5) carrier offset; and 6)symbol timing. In an embodiment, all of these tasks, except for packetstart acquisition, can be performed once at the start of the burst. Forsubsequent PPDUs after the first PPDU of the burst, a partial preamble1312, 1322 is transmitted. The partial preamble 1312, 1322 may be usedby the receiver to perform a packet start acquisition task.

In an embodiment, each PPDU 1300, 1310, 1320 also includes a PHY header1304, 1314,1324, and an SDU 1306, 1316, 1326. Each PHY header 1304,1314, 1324 includes a rate field, in one embodiment, which indicateswhich data modulation rate is used for the payload. In anotherembodiment, the data modulation rate could be determined during atraining exchange.

In addition, each PHY header 1304, 1314, 1324 includes a length/sizefield for the SDU 1306, 1316, 1326 that follows it. Each length/sizefield indicates the length of its associated SDU, in an embodiment. Invarious embodiments, the length/size field can include a number ofmicroseconds, a number of bytes, or some other value indicating length.In the illustrated example, three concatenated PPDUs are shown. More orfewer PPDUs can be sent in accordance with embodiments described inconjunction with FIGS. 13-15. The PHY header 1304 could have a fixed orvariable length.

FIG. 14 is a flowchart of a procedure for a transmitter to transmit aburst of multiple PPDUs, such as those illustrated in FIG. 13, inaccordance with an embodiment of the inventive subject matter. Themethod begins, in block 1402 when the PHY device obtains at least oneSDU. In one embodiment, the SDUs are intermediately or finally destinedfor the same receiver, although it is possible for the SDUs to havedifferent destinations.

In block 1404, the length associated with the next SDU to be transmittedis determined. For example, in an embodiment, the SDU length isrepresented by two bytes. In other embodiments the length field can belarger or smaller. The length is included in the PHY header for thatSDU.

After negotiating access to the air interface, the transmitter transmitsa full-length preamble and the PHY header for the SDU over the air atthe robust modulation rate, in block 1406. In an embodiment, thetransmitter begins transmitting each of the full-length preamble and thePHY header at the beginning of a symbol boundary. In an embodiment, thefull-length preamble is transmitted for two symbols, and the PHY headeris transmitted for one symbol. In other embodiments, either thefull-length preamble or the PHY header can be transmitted for longer orshorter time durations.

When transmission of the PHY header is complete, the transmitterswitches to the data modulation rate, in block 1408. The transmitterbegins transmitting the first SDU, in block 1410. In an embodiment, thetransmitter begins transmitting the first SDU at the beginning of thenext symbol boundary after completion of the PHY header. Alternatively,the first SDU can begin at a time other than a symbol boundary. In otherwords, transmission can begin before or after a symbol boundary.Although not illustrated in FIG. 14, the last symbol in which an SDU istransmitted can be only partially used. In such a case, a gap may existbetween the end of the SDU and the beginning of the next symbolboundary. In addition, internal block padding may be included at the endof each SDU.

In block 1412, the transmitter switches back to the robust modulationrate, so that it will be ready to transmit the next preamble. In block1414, a determination is made whether more SDUs remain to betransmitted. In another embodiment, this determination can be excluded.If more SDUs remain to be transmitted, the transmitter determines thelength of the next SDU to be transmitted, in block 1416.

The transmitter begins transmitting a partial preamble and the PHYheader for the SDU over the air at the robust modulation rate, in block1418. In an embodiment, the partial preamble is transmitted for onesymbol, and the PHY header is transmitted for one symbol. In otherembodiments, either the partial preamble or the PHY header can betransmitted for longer or shorter time durations. In an embodiment, thetransmitter begins transmitting the partial preamble for the next PPDUat the beginning of the next symbol boundary after completion of theprevious SDU. Alternatively, the next PPDU can begin at a time otherthan a symbol boundary. In other words, transmission can begin before orafter a symbol boundary.

After transmitting the partial preamble and PHY header, the methoditerates as shown. Specifically, the transmitter switches back to thedata modulation rate, and transmits the next SDU. After all SDUs in theburst have been transmitted, the method ends.

FIG. 15 is a flowchart of a procedure for a receiver to receive a burstof multiple PPDUs, such as those illustrated in FIG. 13, in accordancewith an embodiment of the inventive subject matter. The method begins,in block 1502, when the receiver detects an incoming, full-lengthpreamble at the robust modulation rate. The receiver uses the preambleto become fully synchronized with the incoming PPDU frame, in block1504. As described previously, full synchronization includes the tasksof: 1) packet start acquisition; 2) channel estimation; 3) antennadiversity and training; 4) receiver automatic gain control (AGC); 5)carrier offset; and 6) symbol timing. In other embodiments, more, feweror different tasks can be performed during a full synchronization.

In one embodiment, the receiver determines the modulation rate of thePPDU's payload from the PHY header, in block 1506. In anotherembodiment, the data modulation rate may be determined during a priortraining exchange.

The receiver also determines the length of the associated SDU from thePHY header, in one embodiment. Once receipt of the PHY header hascompleted, the receiver switches to demodulating at the data modulationrate, in block 1508.

In block 1510, the receiver receives and stores an amount of SDU datawith a length as indicated in the associated length field for the SDU inthe PHY header. In an alternate embodiment, the receiver may determinethat the end of the payload has been reached using a measurement ofsymbol energy.

When the end of the SDU has been reached, the receiver switches back tothe robust modulation rate, in block 1512, so that it will be ready toreceive the next incoming preamble. In addition, in block 1514, thereceiver delivers the SDU. In another embodiment, the receiver can begindelivery of the SDU while the SDU is being received.

After receipt of the first SDU is completed, the receiver determineswhether a partial preamble is detected, in block 1516. If no partialpreamble is detected within an amount of time, the receiver can assumethat the burst is complete, and the procedure ends.

If a partial preamble is detected, the receiver uses the partialpreamble to perform a partial synchronization process, in block 1518. Inan embodiment, this involves performing at least the task of packetstart acquisition. Because at least one of the otherpreviously-performed synchronization tasks need not be repeated, thereceiver will take significantly less time to synchronize with theupcoming PPDU, and the partial preamble can be significantly shorterthan the full-length preamble. In other embodiments, the partialpreamble can be used by the receiver to perform more or other tasks.After partially synchronizing itself, in block 1518, the procedureiterates as shown. Specifically, the receiver receives and processes thePHY header and SDU for the PPDU associated with the partial preamble.

In embodiments described in conjunction with FIGS. 13-15, a partialpreamble and a PHY header are transmitted between SDUs. In anotherembodiment, illustrated in conjunction with FIGS. 16-18, only a PHYheader is transmitted between SDUs, and the intervening preambles areexcluded. Although a preamble is helpful in performing the task ofpacket start acquisition, it is possible to acquire the start of apacket even after loss of structural information by entering a PHYheader search mode, which will be described in more detail inconjunction with FIG. 18, in an embodiment. Accordingly, acceptablesynchronization, error detection, and error recovery may be possibleeven without intervening preambles between SDUs.

FIG. 16 illustrates an example of a timing diagram for transmitting aburst of multiple PPDUs without intervening preambles in accordance withan embodiment of the inventive subject matter. The first PPDU 1600includes a preamble 1602. The preamble 1602 includes a pattern of bits,which the receiver uses to synchronize itself. Subsequent PPDUs 1610,1620 in the burst do not include preambles, in an embodiment.

In an embodiment, each PPDU 1600, 1610, 1620 includes a PHY header 1604,1614, 1624, and an SDU 1606, 1616, 1626. Each PHY header 1604, 1614,1624 includes a rate field, in one embodiment, which indicates whichdata modulation rate is used for the payload. In another embodiment, thedata modulation rate can be determined during a training exchange.

In addition, each PHY header 1604, 1614, 1624 includes a length/sizefield for the SDU 1606, 1616, 1626 that follows it. Each length/sizefield indicates the length of its associated SDU, in an embodiment.Accordingly, the length/size field enables the receiver to determinewhen the end of the SDU will occur, and to predict when the beginning ofthe next PHY header in the burst should occur. In various embodiments,the length/size field can include a number of microseconds, a number ofbytes, or some other value indicating length. In the illustratedexample, three concatenated PPDUs are shown. More or fewer PPDUs can besent in accordance with embodiments described in conjunction with FIGS.16-18. The PHY header 1604 could have a fixed or variable length.

FIG. 17 is a flowchart of a procedure for a transmitter to transmit aburst of multiple PPDUs, such as those illustrated in FIG. 16, inaccordance with an embodiment of the inventive subject matter. Themethod begins, in block 1702 when the PHY device obtains at least oneSDU. In one embodiment, the SDUs are intermediately or finally destinedfor the same receiver, although it is possible for the SDUs to havedifferent destinations.

In block 1704, the length associated with the first SDU to betransmitted is determined. For example, in an embodiment, the SDU lengthis represented by two bytes. In other embodiments the length field canbe larger or smaller. The length is included in the PHY header for thatSDU.

After negotiating access to the air interface, the transmitter transmitsa preamble and the PHY header for the SDU over the air at the robustmodulation rate, in block 1706. In an embodiment, the transmitter beginstransmitting each of the preamble and the PHY header at the beginning ofa symbol boundary. In an embodiment, the preamble is transmitted for twosymbols, and the PHY header is transmitted for one symbol. In otherembodiments, either the preamble or the PHY header can be transmittedfor longer or shorter time durations.

When transmission of the PHY header is complete, the transmitterswitches to the data modulation rate, in block 1708. The transmitterbegins transmitting the first SDU, in block 1710. In an embodiment, thetransmitter begins transmitting the first SDU at the beginning of thenext symbol boundary after completion of the PHY header. Alternatively,the first SDU can begin at a time other than a symbol boundary. In otherwords, transmission can begin before or after a symbol boundary.Although not illustrated in FIG. 17, the last symbol in which an SDU istransmitted can be only partially used. In such a case, a gap may existbetween the end of the SDU and the beginning of the next symbolboundary. In addition, internal block padding may be included at the endof each SDU.

In block 1712, the transmitter switches back to the robust modulationrate, so that it will be ready to transmit the next PHY header. In block1714, a determination is made whether more SDUs remain to betransmitted. In another embodiment, this determination can be excluded.If more SDUs remain to be transmitted, the transmitter determines thelength of the next SDU to be transmitted, in block 1716.

The transmitter begins transmitting the PHY header for the SDU over theair at the robust modulation rate, in block 1718. In an embodiment, thePHY header is transmitted for one symbol. In other embodiments, the PHYheader can be transmitted for longer or shorter time durations. In anembodiment, the transmitter begins transmitting the PHY header for thenext PPDU at the beginning of the next symbol boundary after completionof the previous SDU. Alternatively, the next PPDU can begin at a timeother than a symbol boundary. In other words, transmission can beginbefore or after a symbol boundary.

After transmitting the PHY header, the method iterates as shown.Specifically, the transmitter switches back to the data modulation rate,and transmits the next SDU. After all SDUs in the burst have beentransmitted, the method ends.

FIG. 18 is a flowchart of a procedure for a receiver to receive a burstof multiple PPDUs, such as those illustrated in FIG. 16, in accordancewith an embodiment of the inventive subject matter. The method begins,in block 1802, when the receiver detects an incoming preamble at therobust modulation rate. The receiver uses the preamble to becomesynchronized with the incoming PPDU frame, in block 1804.

At the next symbol boundary after the end of the preamble, the receivershould begin receiving a PHY header. Therefore, the receiver receivesand attempts to validate a segment of data having the size of a PHYheader. In an embodiment, the PHY header size is one symbol width.

Validation is performed by determining if a data integrity field withinthe PHY header correlates with the data in the PHY header. In anembodiment, the data integrity field includes a checksum or CRC, whichenables the receiver to determine whether the data is corrupted oruncorrupted.

A determination is made, in block 1806, whether the PHY header-sizeddata segment includes what appears to be a valid PHY header. If not,then the receiver transitions to a PHY header search mode, indicated byblocks 1808, 1810, and 1812. In this mode, the receiver determineswhether the end of the burst may have been reached, in block 1808. Invarious embodiments, the end of the burst can be determined if no PHYheader is detected within an amount of time, or if a known end point hasbeen reached, or if the symbol energy drops below a threshold. If theend of the burst has been reached, the method ends.

If the end of the burst has not been reached, then the receiver receivesand evaluates each subsequent PHY header-sized segment of data, in block1810. Subsequent segments can be overlapping or sequential.

A determination is made, in block 1812, whether the next PHYheader-sized segment of data appears to be a possible PHY header byvalidating what can be the header data with what can be the headerintegrity field. If the PHY header-sized segment of data does not appearto be a possible PHY header, then the procedure iterates. When apossible PHY header is detected, the receiver discontinues the PHYheader search mode.

When the PHY header search mode is exited, or when the next PHY headerhas been validated, the receiver determines the modulation rate of thePPDU's payload from the PHY header, in block 1814, in one embodiment. Inanother embodiment, the data modulation rate may be determined during aprior training exchange.

The receiver also determines the length of the associated SDU from thePHY header, in one embodiment. Once receipt of the PHY header hascompleted, the receiver switches to demodulating at the data modulationrate, in block 1816.

In block 1818, the receiver receives and stores an amount of SDU datawith a length as indicated in the associated length field for the SDU inthe PHY header. In an alternate embodiment, the receiver may determinethat the end of the payload has been reached using a measurement ofsymbol energy.

When the end of the SDU has been reached, the receiver switches back tothe robust modulation rate, in block 1820, so that it will be ready toreceive the next incoming PHY header. In addition, in block 1822, thereceiver delivers the SDU. In another embodiment, the receiver can begindelivery of the SDU while the SDU is being received.

After receipt of the first SDU is completed, the receiver determineswhether the end of the burst has occurred, in block 1824. If no PHYheader is detected within an amount of time, or if a known end point hasbeen reached, or if the symbol energy drops below a threshold, thereceiver can assume that the burst is complete, and the procedure ends.If a PHY header is detected, the procedure iterates as shown.Specifically, the receiver receives and processes the PHY header and SDUfor the next PPDU.

An embodiment described above in conjunction with FIGS. 16-18 provides ahigh throughput method of burst-mode transmission with robust errordetection and recovery. Throughput is improved from prior art methods byeliminating the IFS and the preambles between SDUs.

The header integrity field of the PHY header enables robust errordetection and recovery. If the receiver determines that PHY data iscorrupted, which can indicate an out of sync condition, the receiver canlook at every byte that follows, to try to find a segment of data thatappears to be a PHY header. If the receiver finds a segment of data thatappears to be a PHY header, the receiver assumes that the datarepresents a PHY header, and the receiver re-synchronizes itself forreceipt of the next SDU.

Thus, various embodiments of a method, apparatus, and system have beendescribed which enable higher throughput data burst transmissions. Theforegoing description of specific embodiments reveals the general natureof the inventive subject matter sufficiently that others can, byapplying current knowledge, readily modify and/or adapt it for variousapplications without departing from the generic concept. Therefore suchadaptations and modifications are within the meaning and range ofequivalents of the disclosed embodiments. The phraseology or terminologyemployed herein is for the purpose of description and not of limitation.Accordingly, the inventive subject matter embraces all suchalternatives, modifications, equivalents and variations as fall withinthe spirit and broad scope of the appended claims.

The operations described above, with respect to the methods illustratedand described herein, can be performed in a different order from thatdisclosed. Also, it will be understood that, although some methods aredescribed as having an “end,” they may be continuously performed.

Although embodiments, above, have been described in conjunction with an802.11 Standard, embodiments can be implemented in conjunction withother standards that have fully or partially “self-describing” frames.In other words, embodiments are not meant to be limited to methods,systems, and devices that implement an 802.11 Standard.

The various procedures described herein can be implemented in hardware,firmware or software. A software implementation can use microcode,assembly language code, or a higher-level language code. The code may bestored on one or more volatile or non-volatile computer-readable mediaduring execution or at other times. These computer-readable media mayinclude hard disks, removable magnetic disks, removable optical disks,magnetic cassettes, flash memory cards, digital video disks, Bernoullicartridges, random access memories (RAMs), read only memories (ROMs),and the like.

Embodiments of the inventive subject matter may pertain to any of avariety of types of PHY layers that support an IEEE Std 802.11 and otherWLAN standards, including but not limited to, infrared (IR) basebandPHY, frequency hopping spread spectrum (FHSS) radios (e.g., in the 2.4GHz band), direct sequence spread spectrum (DSSS) radios (e.g., in the2.4 GHz band), orthogonal frequency domain multiplexing (OFDM) radios(e.g., in the UNII bands), and other types of PHY layers for which IEEEStd 802.11 and other WLAN standards are being extended to now and in thefuture. Further, embodiments of the inventive subject matter can be usedin conjunction with any IEEE Std 802.11, including IEEE Std 802.11-1997,802.11a, 802.11b, 802.11e, other variants of the IEEE Std 802.11existing or being developed now or in the future, and other WLANstandards besides IEEE Std 802.11.

In the claims, the terms “first modulation rate” and “second modulationrate” are used. It is to be understood that these modulation rates canbe the same or different from one another.

1. A method comprising: receiving a frame containing a single preambleand a header over an air interface at a first modulation rate; andreceiving a consolidated payload in the frame, at a second modulationrate different from the first modulation rate, wherein the consolidatedpayload includes multiple service data units; wherein the consolidatedpayload further includes information indicating when an end of each ofthe multiple service data units will occur; wherein the informationincludes multiple delimiters, each delimiter preceding an associated oneof the multiple service data units and including an indication of alength of the associated service data unit; wherein a particular one ofthe delimiters further includes a validation field, the method furthercomprising determining whether the particular delimiter is valid usinginformation in the validation field, and if the particular delimiter isnot valid, finding another delimiter received in the consolidatedpayload and receiving another service data unit associated with saidanother delimiter.
 2. An apparatus comprising: a medium access controldevice, to receive multiple service data units from a physical device;and the physical device, coupled to the medium access control device,which is operable to receive a frame containing a single preamble and aheader over an air interface at a first modulation rate and to receive aconsolidated payload in a same frame as the header at a secondmodulation rate different than the first modulation rate, wherein theconsolidated payload includes the multiple service data units; whereinthe consolidated payload further includes information indicating when anend of each of the multiple service data units will occur, theinformation further including multiple delimiters, each delimiterpreceding an associated one of the multiple service data units andcontaining an indication of a length of the associated service dataunit; wherein each delimiter further includes a validation field, andthe physical device is further operable to determine whether aparticular delimiter is valid using information in the validation fieldof the particular delimiter, and to find, if the particular delimiter isnot valid, another delimiter received in the consolidated payload afterthe particular delimiter and to receive another service data unitassociated with said another delimiter.
 3. The apparatus of claim 2,further comprising one or more antennae, coupled to the physical device,which are operable to provide an interface between the air interface andthe physical device.
 4. A computer-readable medium having programinstructions stored thereon to perform a method, which when executedwithin a wireless local area network device, result in: receiving aframe containing a single preamble and a header over an air interface ata first modulation rate; and receiving a consolidated payload in theframe at a second modulation rate different than the first modulationrate, wherein the consolidated payload includes multiple service dataunits; wherein the consolidated payload further includes informationindicating when an end of each of the multiple service data units willoccur; wherein the information includes multiple delimiters, eachdelimiter preceding an associated one of the multiple service dataunits, each delimiter including an indication of a length of theassociated service data unit; wherein each of the delimiters furtherincludes a validation field, and executing the program instructionsfurther results in determining whether a particular delimiter is validusing information in the validation field of the particular delimiter,and finding, if the particular delimiter is not valid, another delimiterreceived after the particular delimiter in the consolidated payload andreceiving another service data unit associated with said anotherdelimiter.